New World Monkeys: Callitrichids

Scientific Name1

Common Name



Callithrix jacchus

common marmoset

Cebuella pygmaea

pygmy marmoset



Leontopithecus sp.

lion tamarin

Leontopithecus rosalia

golden lion tamarin

Saguinus fuscicollis

saddle-back tamarin

Saguinus labiatus

red-bellied tamarin

Saguinus oedipus oedipus

cotton-top tamarin

Saguinus oedipus geoffroyi

Geoffroy's tamarin

Callimico goeldii

Goeldi's monkey

New World monkeys (Ceboidea) are generally divided into marmosets and tamarins (Callitrichidae) and the "true" monkeys (Cebidae). The callitrichids are distinct from the cebids in having claws on most digits other than the great toe


This is a list of scientific and common names of species discussed in this chapter, not a comprehensive taxonomic list.

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--> 6— New World Monkeys: Callitrichids Scientific Name1 Common Name Marmosets   Callithrix jacchus common marmoset Cebuella pygmaea pygmy marmoset Tamarins   Leontopithecus sp. lion tamarin Leontopithecus rosalia golden lion tamarin Saguinus fuscicollis saddle-back tamarin Saguinus labiatus red-bellied tamarin Saguinus oedipus oedipus cotton-top tamarin Saguinus oedipus geoffroyi Geoffroy's tamarin Callimico goeldii Goeldi's monkey New World monkeys (Ceboidea) are generally divided into marmosets and tamarins (Callitrichidae) and the "true" monkeys (Cebidae). The callitrichids are distinct from the cebids in having claws on most digits other than the great toe 1   This is a list of scientific and common names of species discussed in this chapter, not a comprehensive taxonomic list.

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--> (hallux) and having two, rather than three, permanent molars. Goeldi's monkey (Callimico goeldii) has claws but also three molars, and some authorities prefer to consider it with the cebids; but we consider it with the marmosets and tamarins because all display the common adaptation of climbing main trunks with the aid of claws. All callitrichids are small arboreal primates ranging from Costa Rica to southern Brazil and Bolivia in nature. The smaller forms, like the pygmy marmoset (Cebuella), at about 120 g (4 oz), subsist mainly on insects and tree saps obtained from gouge holes; medium-size marmosets, at 300–400 g (11–14 oz), and the larger tamarins (Saguinus and Leontopithecus) and Goeldi's monkey, at 600–1,000 g (1.3–2.2 lb), are more omnivorous, but marmosets are also heavily dependent on exudate feeding (Rylands 1993). Marmosets are often distinguished from tamarins by their procumbent incisors; tamarins also have more robust and longer canine teeth. Comprehensive descriptions of the natural history, behavior, and communication of callitrichids can be found in Rylands (1993) for marmosets and tamarins, Soini (1988) for pygmy marmosets, Stevenson and Rylands (1988) for marmosets, Snowdon and others (1988) for tamarins, Kleiman and others (1988) for lion tamarins, and Heltne and others (1981) for Goeldi's monkey. The reproductive biology and captive breeding of marmosets and tamarins are summarized in Hearn (1983). Housing The ideal captive environment is conducive to good physical health, provides for successful reproduction and the raising of offspring, and enables animals to acquire the behavioral skills that they would need in their natural environment (Snowdon and Savage 1989). The size and, perhaps more important, the furnishings of the captive environment affect the behavior of callitrichid monkeys (Box 1988; Caine and O'Boyle 1992; Chamove and Rohrhubert 1989; Molzen and French 1989). Most studies have dealt with the positive effects of well-constructed environments on behavior, but Schoenfeld (1989) described the impoverishing effects of a drastic reduction in environmental complexity on social behavior and infant care in a family group of common marmosets. Large cages, containing branches and other substrates for climbing, have been used successfully in many long-term breeding colonies. They promote physical well-being and meet the behavioral needs of laboratory primates. Caging should permit callitrichids to assume normal body postures (e.g., sitting on a support with the tail hanging down without touching the cage floor) and to engage to some extent in normal locomotor behavior, such as climbing, running, and jumping. Wild marmosets and tamarins only occasionally descend to the ground and in captivity prefer to be above caregiving personnel (Poole 1990). Therefore, it is

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--> advisable not to house these primates in two-tier cages. There are reports of less activity and poorer reproductive performance when animals are housed in the lower tier of a two-tier cage system (Heger and Neubert 1988; Scott 1989). When space is at a premium, narrow, high cages are preferred over wide, low cages placed one on top of the other. An alternative to providing tall cages is to suspend cages from the ceiling, so that there is space between the cage floor and the floor of the room. Covering the cage floor with wood chips or shredded paper substantially increases the use of the floor by common marmosets and cotton-top tamarins (McKenzie and others 1986). Marmosets and tamarins might be reluctant to retrieve food from the cage floor. If tall cages are used (say, 2 m, or 6.6 ft, high), animals rarely descend to less than 0.5–1 m (1.6–3.3 ft) above the floor. Therefore, food and water should be offered on a feeding platform or in a bowl placed high in the cage and in a position that avoids contamination from feces and urine. If small cages are used, it is beneficial to provide a large exercise cage for temporary use. One method of increasing the effective space is to use transparent air-conditioning ducting attached to the side of cages (Hearn 1983). Animals can be trained to move voluntarily through the ducting to enter other cages or transport cages, thus minimizing the stress of handling. Animals that are removed from groups because of illness or behavior problems can still be allowed close visual access through the ducting. Finally, a loop of ducting running from one side of the cage around the back or over the top to the opposite side creates a runway that is frequently used by juveniles and subadults in play. The nature of the furnishings in the cage appears to be even more important than the absolute amount of space in facilitating species-typical behavior. It is desirable to have a variety of wooden or fiber structures in a cage. Branches and ropes allow animals to display manipulative behavior and a range of natural movements, including leaping from branch to branch. Such cage furnishings will need to be replaced every 2–3 months as they wear out (e.g., bark stripped from branches) and as necessary to maintain sanitation. Panels can be used to divide the cage into visually shielded compartments; this allows submissive animals to move out of sight of dominant cagemates. The nest box can be provided with a locking door to double as a transport box when required. Chemical communication by means of scent marking is important in the sexual and social behavior of all callitrichids (Epple 1986). Branches are the normal substrate for scent-marking with urine and the secretions from specialized scent glands. Animals that are provided only with smooth, nonabsorbent surfaces, such as stainless steel or plastic, scent-mark these surfaces. The sticky, lipid-containing marks coating the surfaces of smooth objects tend to soil the animals' fur. The amount of scent-marking behavior varies among species and even among individuals of the same species. Therefore, a cage-washing schedule that constitutes a compromise between the need for sanitation and an intact odor environ-

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--> ment will have to be worked out on an individuals basis. Cages can be sanitized on a regular but less frequent schedule than might be used for other animals. It is still advisable to exclude at least one perch or the nest box when the cage is washed so that some of the social odor is retained. Animals that have to be housed in small cages should be provided with environmental enrichment devices for the development of behavioral and ecological skills (Poole 1990; Scott 1989). Successful enrichment devices are ones that make use of the natural exploratory and foraging behavior of the animals. The use of artificial gum trees (McGrew and others 1986) can be used effectively for Callithrix jacchus in that it stimulates species-typical activity (see also Molzen and French 1989). Simple, disposable objects can stimulate long periods of activity. Juveniles mainly, but also adults, explore small cardboard boxes, play in and around them, and eventually tear them to shreds. A large plastic bottle (e.g., a gallon milk jug) that has a large opening cut into it and is suspended by the handle has a similar effect. Paper towels and even toilet paper stimulate activity: the animals tear them apart and compete for possession of the shreds. The social and territorial behavior of marmosets and tamarins needs to be taken into account in designing appropriate housing. Under most environmental conditions, wild callitrichids are highly territorial. Under crowded colony conditions, they display high levels of threat behavior toward other visible groups. Moreover, high levels of abortion and infant loss have been reported in captive colonies of some species, such as cotton-top tamarins (Glatston and others 1984; Kirkwood and others 1983; Scullion 1987) and saddle-back tamarins (G. Epple, Monell Chemical Senses Center, unpublished data), and it has been suggested that these problems are related to chronic arousal caused by the proximity of neighboring groups in a colony situation. When several groups are housed in the same room, visual baffles placed between adjacent cages usually appear to be sufficient to reduce threat displays and aggressive behavior, even though animals in one cage can hear and smell other groups of animals; but Epple (unpublished data) found in necessary to install sound-absorbing baffles in a large colony of saddle-back tamarins to reduce the noise that was amplified by the painted concrete surfaces of the room. In contrast, Johnson and others (1991b) found that cotton-top tamarin groups housed in visual contact with other conspecific groups had better infant survival than groups housed in visual isolation; the cages were similar in the two conditions. These observations show the importance of careful evaluation of specific colony situations and of species, as well as individual requirements, by colony managers. Another means of reducing the arousal caused by housing several groups of the same species in proximity is to place groups of different callitrichid species next to each other. Associations between different callitrichid species occur regularly in nature (Castro and Soini 1977; Heymann 1987; Pook and Pook 1982; Terborgh 1983). Polyspecific groups often travel together and share territories but do not compete with each other socially.

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--> Because of their natural social organization (see "Social Behavior," below), it is recommended that callitrichids and Goeldi's monkeys be maintained in stable male-female pairs or small family groups. Nonrelated adults of the same sex should not be housed together unless they are very familiar with each other and no adult of the other sex is present. If breeding is not desired, same-sex siblings can live together. In cases where a conspecific companion is not available, the monkeys can be housed with a companion from a related species of callitrichid. Captive animals engage in many normal social activities with companions belonging to related species. If single-cage housing is unavoidable, it might be possible to house pairs in adjacent cages and provide either full visual contact or a "contact window" that allows some social interactions between familiar individuals. If singly housed animals are given temporary access to a companion, the same animals should always be placed together. Colony managers have found that some animals cannot be successfully paired with a social companion, because of either extreme aggression or extreme submissiveness. Therefore, the type and degree of social stimulation provided to animals should be carefully monitored. Nutrition Wild marmosets, tamarins, and Goeldi's monkeys consume a varied diet that includes tree exudates (sap or gum), fruits, buds and flowers, nectar, insects, and small vertebrates. Much of their time is spent in foraging. Marmosets and pygmy marmosets have specialized dentition for gouging holes in trees from which exudate can be extracted and in the wild obtain much of their food that way. Foraging for tree gums takes up most of the time of wild pygmy marmosets (Soini 1988), and the contribution of gum to the diet of the more frugivorous-insectivorous marmosets varies among species (Stevenson and Rylands 1988). Captive Cebuella and Callithrix species produce gouge holes in every material that they can manage to chew. Natural branches in the cage will not only provide the normal substrate for this important activity, but also direct the animals' attention away from materials that might damage their teeth. McGrew and others (1986) designed a sap feeder made of wooden doweling with holes drilled inside that was filled with gum arabic. Common marmosets quickly learned to excavate holes in this feeder to obtain gum. Tamarins lack the dentition to create exudate flows themselves, but they use exudate flows created by other animals. Young monkeys, at about 4 weeks of age, begin to beg for solid food from animals that carry them. They obtain most of their food from other group members, which share food with them for several months. During this time, the youngsters seem to learn to recognize the group's food spectrum and to distinguish between wholesome and unwholesome foods. That experience might influence food selection and preferences later in life. The natural diet marmosets and tamarins contains high concentrations of

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--> proteins, and protein requirements for these species have been estimated at around 20% (Tardif and others 1988). Coprophagia has been reported to be associated with lower percentages of dietary protein (Flurer and Zucker 1988). Most laboratories housing callitrichids feed a commercial diet high in protein (25%) to substitute for the highprotein content of insects. Vitamin D3, found in insect chitin, is important in promoting absorption of calcium and other minerals. Callitrichids cannot metabolize vitamin D2, so diets fed to them in captivity should have adequate concentrations of vitamin D3 (Hunt and others 1967a, b). Many colonies use lighting that mimics the full spectrum of sunlight to promote vitamin D3 synthesis and absorption. Several laboratories have maintained colonies on unsupplemented single diets. Such diets might fulfill all the nutritional requirements of these primates, but they do not always appear to be palatable enough to be eaten by all individuals in sufficient amounts. Primates that naturally forage on a large variety of foods are adapted to variety and might need variety to stimulate intake. In many colonies, additional feedings of high-protein foods—such as cottage cheese, yogurt, chicken, ground beef, and mealworms—are provided early in the morning and in late afternoon. A variety of fruits and high-protein foods also will accommodate individual dietary preferences and allow each individual access to some highly preferred foods while maintaining overall nutritional balance. Individual food preferences should be carefully monitored. Although most animals will consume a balanced diet when given a choice among foods, some might reject all other foods in favor of fruit. For such animals, it is advisable to exclude fruit from the first feeding of the day and provide it in the late afternoon. All fruits and vegetables should be carefully washed before feeding them to the monkeys. Animals 15 years old or older often have dental decay or loss of teeth and might be unable to eat hard pellets. They must be provided with food that they can chew. Aged animals might also have special nutritional requirements, such as an increased need for vitamins. Marmosets and tamarins are small animals with a high metabolic rate. In the wild, animals sleep in hidden locations for 13 hours per night. Feeding rates are high in the hours before sunset and immediately after animals arise in the morning. It is important that captive animals have fresh food available early in the morning and in late afternoon. Social Behavior All callitrichids are social, but most live in small groups, which often consist of a single reproductively active pair and their offspring. In wild populations, some variability has been noted, but except for Goeldi's monkeys, which do well with more than one breeding female present, a single breeding pair and their offspring do best in captivity. The skin of marmosets, tamarins, and Goeldi's monkeys contains specialized

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--> scent glands. Glands are typically found in the anogenital region, the suprapubic area, and above the sternum and possibly on the face at the borders of the mouth. The oily secretions from these glands, mixed with urine and genital discharge, are deposited on all items in the animals' environment, and in some species on the bodies of cagemates, through scent-marking behavior. Different species use different glands for scent-marking; moreover, the context in which scent-marking is exhibited varies somewhat among species. Geoffroy's tamarins, cotton-top tamarins, and Goeldi's monkeys also show a self-marking behavior. The scent marks are important components of the communication systems of these primates. The marks can contain information on species, subspecies, and individual identity, on hormonal condition, on social rank, and on the age of the scent. Scent communication plays a role in a variety of social and sexual interactions and in attachment between group members and the infants that they care for. Scent from a breeding female also contributes to the suppression of ovulation in nonbreeding females of several species. As is true of other mammals, monkeys might feel comfortable in their home environment with their own scents present (Epple and others 1993). Scent-marking rates increase when conspecific intruders are present and during territorial encounters. The close proximity of neighboring groups in a colony situation can arouse some animals so strongly that they scent-mark excessively, soiling themselves and their cagemates. In such cases, the problem can sometimes be corrected by switching neighbors or placing the animals next to a group of another callitrichid species or an empty cage. Reproduction and Development Callitrichids and Goeldi's monkeys typically show little or no sign of estrus and no obvious changes in outward physical appearance or in vaginal cytology during estrus. Estimation of gonadotropins and of ovarian steroids in blood, urine, or feces shows that female ovulatory cycles vary greatly, from 15 to 28 days. Mating behavior does not closely reflect a female's hormonal state. Mating might peak during the periovulatory phase but also occurs at other times, even during pregnancy, when a period of behavioral receptivity can occur. Mating is typically very quick. Mating solicitation is indicated by rapid tongue flicking and looking over the shoulder by the female, and both partners might tongue flick during copulation (Epple 1978). Callitrichids have been assumed to be monogamous (one male mating with one female), but the results of several recent field studies have found both polyandry (one female mating with more than one male) and polygyny (one male mating with more than one female). However, a survey of captive cotton-top tamarin colonies found few departures from monogamy, and the departures did not lead to stable breeding conditions (Price and McGrew 1991). Under captive conditions, callitrichid groups contain a single breeding female. Reproduction is

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--> suppressed by means of behavioral or physiological mechanisms in all other females, although mating might occur (see below for details). In some species, trios consisting of two males and one female have been maintained, but one male has quickly become subordinate to the other. Peer groups of young marmosets can be formed (Abbott and others 1989; Barrett and others 1990) but such groups need to be carefully monitored because levels of aggression are generally high in the first hours and some animals might have to be removed. The groups quickly stabilized with one male and one female taking the dominant breeding position. The gestation period varies: about 129 days in golden lion tamarins; 140–150 days in common marmosets, pygmy marmosets, saddle-back tamarins, and Goeldi's monkeys; and up to 184 days in cotton-top tamarins. In both wild and captive populations, twin births are the norm, although triplets are sometimes seen. All marmosets and tamarins tend to exhibit a postpartum estrus, but the extent to which this results in a new pregnancy varies among species. In cotton-top tamarins, the period from parturition to postpartum ovulation is affected by the number of infants being nursed. Females with one or no surviving infant ovulate sooner than females with twins. Females that typically nurse both twins at once have an earlier postpartum ovulation than females that nurse each twin separately (Ziegler and others 1990). Infant callitrichids are carried full time for the first month of life. They normally cling to the neck and shoulder region of their carrier. Infants that cling to the hips or to the ventral side of the carrier are usually weak, and tails hanging down limply instead of curling against the carrier's body can also be a sign of weakness. Weak infants should be monitored carefully. In Goeldi's monkeys, ventral carrying of an infant during the first week of life seems to be normal. The breeding system of callitrichids is cooperative, involving both parents and other group members in the care of infants. Pregnant females should, therefore, never be housed alone. If the breeding male dies or has to be removed, the female should be placed with another male. An experienced male that is placed with a pregnant female will help the female to raise her offspring. There is great variability within and between species in the patterns of parental care, but both mothers and fathers are actively involved in infant care from the earliest ages. Siblings also become involved in infant care; males are generally more involved than females. Various investigators have observed competition between group members for access to infants. In a moderate-size family group, the mother is rarely observed carrying infants except during nursing. Infants begin to make brief forays away from their carriers within 4–6 weeks. They start eating solid food at about 4–6 weeks, often begging food from adults, and they can be completely independent of care from group members by 10 weeks. With the birth of new infants, 5- to 7-month-old siblings become active as playmates; with the birth of another set of infants, these animals, now juveniles, become actively involved as infant caregivers. Especially for tamarins, this experience is very important for the development of appropriate parental behav-

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--> ior (Snowdon 1996). Animals that never participate in the care of younger siblings might kill or neglect their own offspring once they start to breed. Animals that are assigned to become breeders, therefore, should be left with their own parents at least until the next two sets of younger siblings have been weaned. Animals that are removed from their parents at an earlier age because the development of parental skills is unnecessary can be successfully socialized in small peer groups consisting of juvenile males and females. Under captive conditions, some animals can be kept in their natal groups for indefinite periods. Animals that are 5 years old can still take a subordinate role within their family. However, animals (generally of the same sex) can start harassing one another quite suddenly, and this requires removal of one or both animals. Such behavior is quite unpredictable. Parents generally do not intervene in the fights and harassment's among offspring. Once animals are mated, there are rarely any signs of tension or conflict between mates, and they can remain together for the rest of their lives. Some callitrichids survive in captivity for more than 20 years. In the cooperative breeding system of callitrichids, reproduction is suppressed in all female group members but one. Reproductive suppression is achieved either by suppression of sexual behavior or by suppression of ovulation, probably through a combination of pheromonal cues from the breeding female and nonspecific behavioral cues (Abbott and others 1989; Barrett and others 1990; Epple and Katz 1984; French and Stribley 1987; Savage and others 1988; Ziegler and others 1987). In common marmosets, about 50% of the families studied by Abbott and Hearn (1978) had a daughter that ovulated, although none became pregnant. In contrast, in peer groups only one female ever ovulates (Abbott and others 1990). In cotton-top tamarins, but not in common marmosets, after removal of a noncycling female from her group, stimulation by a novel male is necessary to induce ovulation (Widowski and others 1990). Female cotton-tops housed alone or with brothers fail to ovulate. The mere sight, smell, and sound of a novel male suffice to induce ovulation. Once ovulation has begun, it can continue in the absence of a male (Widowski and others 1992). In golden lion tamarins, subordinate females' estrogen cycles are synchronized with those of the reproductive female, but with much lower estrogen concentrations; however, they do not become pregnant (French and Stribley 1987). Johnson and others (1991a) reported extreme reproductive suppression—including reduced parity, reduced number of live births, and increased spontaneous abortions—during a period when a common marmoset colony was disturbed by nearby building construction. G. Epple (unpublished data) experienced identical problems with a breeding colony of saddle-back tamarins. Those observations suggest that breeding callitrichids should be isolated from loud noises and other disruptions.

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--> Cognition Marmosets and tamarins have well-developed visual, olfactory, and auditory perceptual skills. Saddle-back tamarins can recognize former social partners even after separations of several years (Epple and Niblick 1997). Formal tests of cognition have often failed to provide evidence of cognitive abilities, possibly because removal of animals from social groups for testing is highly disruptive. However, Savage and others (1987) successfully tested color discrimination in cotton-top tamarins by moving the test apparatus to the home cage. Eglash and Snowdon (1983) with pygmy marmosets and Hauser and others (1995) with cotton-top tamarins have found evidence of precursors of the mirror self-recognition of apes. Hauser (in press) and Hauser and Carey (1998) have studied expectations about objects and events, including numerosity and understanding of causality in cotton-top tamarins. When tested appropriately, the cognitive abilities of callitrichids are highly developed. Callitrichids living in a naturalistic environment seem to maintain a ''cognitive map" of their environment and detect even minor changes. Under such conditions, neutral novel objects can stimulate little interest, and attempts to provide for environmental enrichment have been disappointing. Saddle-back tamarins living in a greenhouse habituated quickly to novel objects, usually in less than 15 min. Reintroducing the same objects 3 months later failed to produce any sign of interest (Menzel and Menzel 1979). Novel objects themselves might not be effective, but enrichment devices that allow animals to remain actively involved with searching for food items (Molzen and French 1989) do effectively encourage sustained activity and might be good enrichment devices (Box 1988; McGrew and others 1986; Molzen and French 1989). Personnel Marmosets and tamarins recognize individual humans on the basis of odor (Cebul and others 1978), voice, and appearance. Callitrichids can develop strong likes and dislikes of individual humans. The monkeys appear to have long memories and respond with fearful behavior to hearing the voice or footsteps of someone who has captured them several months earlier. Curiously, personnel in several colonies have found that shoes might be an important element of an individual caregiver's appearance. On the basis of this anecdotal evidence, it might be wise for caregivers to wear the same shoes, lest the animals become agitated. Colony managers have observed that hand-raised animals socialized to people can become overaggressive, especially when the animals reach puberty. Personnel whose primary experience is with other species need to know about the cooperative breeding, twinning, and extensive caretaking by fathers and other group members. They should learn some of the important vocalizations

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--> and behavioral patterns of callitrichids so that they can diagnose potential problems from behavioral observations. Familiarity of the monkeys with their caregivers is extremely valuable, particularly in breeding colonies, because parents with newborn infants are easily alarmed by unfamiliar humans and if so alarmed might neglect or attack their babies. Capturing should be avoided as much as possible. Clear discriminative stimuli, such as different-color coats or uniforms, worn when handling is necessary can help monkeys to predict and discriminate the handling event and thus prevent generalization to caregivers performing routine colony tasks. The presence of a familiar technician who does not participate in the capture itself might be helpful in calming animals that have been captured. If handling is necessary, the animal in question should first be removed from the colony room. The distress vocalizations of monkeys that are caught and handled tend to arouse the entire colony room and in some species can cause prolonged symptoms of stress, such as diarrhea. Frequent handling might be avoided in some species, such as the common marmoset, by training the animals to accept medications with rewards of preferred food (Hearn 1983). However, tamarins appear to be more excitable and less amenable to training than marmosets. Responses can differ between individual animals, so various catching methods, such as locking the animals in the nest box and removing them from there or using a small net, are useful. A net might be useful for these animals because the animals tend to associate being handled with the net rather than with the person who catches them. The use of nets, however, should be undertaken with caution because animals can be injured by the hoops and handles of nets or by becoming entangled in the nets themselves. Veterinary Care Veterinarians should be experienced in handling small animals that have high metabolic rates. Because of their high metabolism, animals that become sick can deteriorate quickly. An animal can appear in good health in the morning, show signs of sluggishness or ataxia in the afternoon, and die by the following morning. Animal care personnel should be trained to monitor behavior for signs of illness. Signs include chronic piloerection, sluggishness, ataxia, diarrhea, lack of appetite, dull and sunken eyes, weight loss, and changes in routine behavior. They are usually noticeable only by human observers who are familiar with the individual monkey. Marmosets and tamarins can be trained to step on the platforms of remote reading scales, and regular weighings are possible. Technicians can monitor the physical well-being of the animals through these weights, and interventions can be undertaken for animals that show substantial loss of weight. Therefore, well-trained and concerned animal technicians are invaluable to the veterinarian. They can alert the veterinarian to health problems or behavioral problems (for ex-

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--> ample, stress due to severe dominance relationships between animals). A familiar technician can calm the animals during treatment and can administer many medications topically or orally in food without the need for handling the animals. The feeding of high-protein snacks each morning and each afternoon not only increases the protein content of the diet, but allows animal care staff to monitor the animals more often. Marmosets and tamarins are susceptible to a number of human diseases, including measles, mumps, and cold sores caused by Herpesvirus simplex . These disease agents can cause potentially fatal infections. Herpesvirus saimiri is carried by squirrel monkeys; although it is not associated with any disease in these monkeys, it causes leukemia or malignant lymphoma in callitrichids, so marmosets and tamarins should not be housed in a room that contains squirrel monkeys (Adams and others 1995). Callitrichids and cebids should not be housed together, because of risk of disease transmission (Bennett and others 1995). A "wasting syndrome" has been described in many species of captive callitrichids that includes such symptoms as weight loss, anemia, colitis, and extensive diarrhea; but there appear to be great differences in susceptibility between colonies of the same species and no clear agreement about the etiology. Suggested etiologies have involved nutrition, infectious agents, and environmental social stress; in cotton-top tamarins, spontaneous adenocarcinoma of the colon has been described. Some colony managers have found that the condition of some animals experiencing apparent social stress can be improved by moving the affected animals to a new social environment (Knapka and others 1995; Morin 1983).